1. Field of the Invention
The present invention relates to contact ferrules for high voltage fuses, and more particularly, to the unique method of making ferrules having integrally formed locating bosses.
2. Description of the Prior Art
High voltage expulsion type fuses are well known in the art as exemplified by U.S. Pat. Nos. 3,267,232--Barta, 3,176,100--Barta, 3,575,683--Fahnoe, and 3,855,563--Cameron. Such high voltage expulsion fuses typically are mounted in dropout type mountings so that when the fuse operates, the fuse "drops out" of the mounting under the force of gravity to visually indicate fuse operation. Dropout type fuse mountings are typically specially adapted for this purpose, and it is necessary to mount on one end of the end of the fuse a trunnion assembly which engages the lower dropout mounting and mount a fuse release mechanism on the other fuse which engages the upper dropout mounting. Since such terminal mountings are typically permanently installed in the field, it is necessary for the fuse to be specifically dimensioned to fit these mountings. Further, since the exact dimensional relationship between the upper and lower terminal mountings is fixed, it is necessary that when the trunnion assembly and fuse release assembly are mounted on the fuse, these assemblies have the desired positional relationship which will permit them to be installed into the fuse mounting. To achieve this purpose, the prior art fuses have had a locating boss on the lower ferrule which engages a slot on the trunnion assembly. At the upper end of the fuse, a locating slot is formed in the side of the insulator tube which will engage a pin on the fuse release assembly to properly position and orient that assembly.
Heretofore, in prior art fuses, the locating boss on the lower ferrule has been provided by drilling a hole through the ferrule and installing a metal pin or rivet through the hole. The pin or rivet is then soldered to effectuate a moisture tight seal since such fuses are typically hermetically sealed to prevent moisture from entering the fuse. However, since the locating boss is a projection which can experience external forces from the trunnion assembly as well as during handling, it is possible that the solder seal around the pin or rivet may be broken so that a small leak may develop around the locating boss. Such small leaks are undesirable since any leak, regardless of how small, can result in the ingress of moisture into the fuse with resultant damage or deterioration to the interior components.
Further, since it is necessary to provide a correct positional relationship for the locating boss, it is extremely difficult to pre-drill the holes for the rivets or pins prior to installation of the ferrule on the fuse since the position of the ferrule may vary as a result of assembly techniques.
Also, it is difficult to provide non-circular shaped rivets or pins when it is desirable to employ non-circular locating bosses to control interchangeability between different types of fuse units and trunnion assemblies.
Thus, it would be a desirable advance in the art to provide an integral leak-free locating boss of a predetermined shape on a lower ferrule of a high voltage fuse which can be correctly positioned after the ferrule is installed on the fuse.